In the optical and microelectronics fields many currently available coatings suffer from numerous drawbacks and inconsistent properties. Among the drawbacks there may be mentioned for example, low dielectric strength, poor physical durability, poor transparency or a very narrow band gap of transparency, moisture absorption, inadequate chemical resistance and the like.
Recently, considerable interest has developed in diamond-like carbon films for such optical and microelectronics applications because of their more desirable properties, in some respects, which is attributable to the heterophase structure of the films.
Among the highly desirable and useful properties that diamond-like carbon films are expected to possess there may be mentioned, for example, high transparency in the UV, visible and infra-red wavelengths, an index of refraction and hardness approaching that of diamond, strong adhesion to substrates, high dielectric strength and chemical inertness. Until now, to the best of our knowledge, diamond-like carbon film have only exhibited some of these properties simultaneously.
It is recognized that diamond-like carbon films are grown when carbon is deposited in a low-temperature plasma, at which time the high pressures and temperatures, necessary for forming the diamond-like structure, are achieved by collisions with a substrate surface by particles having high kinetic energy. Previously diamond-like carbon films have been produced by rf sputtering, "ion plating" and "plasma decomposition" processes. However, most of the film growth conditions and the resulting films are not well defined due to inadequate understanding of the factors controlling the ion energy. As a result diamond-like carbon film of defined properties and characteristics have not been able to be produced on a reproducible basis. Nor has it been possible to produce diamond-like carbon films exhibiting most of all of the aforementioned desirable properties and characteristics.
Previously, plasma decomposition reactions employing a hydrocarbon product gas, such as methane, ethane, propane and isobutane, as the carbon source have been utilized. However, in such plasma decomposition processes, the saturation partial pressure of the product (i.e. its equilibrium concentration near the deposited film) must be markedly exceeded to drive the deposition reaction. Yet, the risks are undesirable homogeneous decomposition of the product gas to carbon and/or other involatile species in the reactor volume, potentially causing carbon to rain on the surface of the substrate rather than producing the desired heterogeneous growth process on the substrate surface. This is more likely to result in softer amorphous films with more inclusions and poor adhesion.
It is therefore highly desirable that a process be made available whereby diamond-like carbon films are produced without said drawbacks. It is likewise desirable that an improved process for depositing diamond-like carbon films be provided which produces diamond-like carbon films of improved and more uniform properties and characteristics. It is also most desirable that a process be provided where unwanted homogeneous production of carbon in the reactor is avoided or substantially eliminated.